New Mexico Geological Society Annual Spring Meeting — Abstracts

 The Hermit’s Peak granite is a 1.70 Ga biotite-granite in the southern Sangre de Cristo Mountains of northern NM. It is located within a broad area that records both Yavapai and the later Mazatzal deformation, referred to as the Yavapai-Mazatzal transition zone. The goals of this study are to map mineral, textural, and structural variations throughout the Hermit’s Peak granite in order to address its size and shape, how the granite was emplaced, and how it figures into the assembly of Proterozoic provinces. This tabular, northwest-trending pluton covers approximately 32 km² of the central Las Vegas Range. The composition of the Hermit’s Peak granite varies slightly throughout, typically displaying euhedral to subhedral 1-2 mm sized grains and ranging from syenogranite to monzogranite. The granite intrudes Paleoproterozoic metamorphosed country rock at the western and northern most extents, with a moderate to strong foliation dipping, on average, to the SW and paralleling the strong foliations seen in the country rock. Along its eastern and southern exposures, the pluton is juxtaposed against Pennsylvanian aged sedimentary units along the Hermit’s Peak thrust fault. Fabric development is defined by an alignment of biotite and is variable across the intrusion, but is generally strongest at the margins and weakest in the center. The foliation at the southwestern contact is defined by compositional bands that petrographic analysis reveals to contain primarily curvo-planar grain boundaries with some serrated quartz. An additional facies within 1.5 km of this contact displays serrated feldspar boundaries and ribboned quartz grains, paralleling a biotite foliation that developed in the transition between magmatic to submagmatic state. These data are most consistent with the synkinematic emplacement of the Hermits Peak granite.